1. Field of the Invention
The embodiments of the invention generally relate to high speed data communications protocols, and, more particularly, to Fiber Channel Protocol (FCP) and Fiber Connectivity (FICON) links and including, but not limited to, such protocols such as Ethernet for networking, storage and related applications.
2. Description of the Related Art
Across the data communication industry, Fibre Channel Protocol (FCP) and Fiber Connectivity (FICON) protocols are used for networking, storage, and related applications. It will be understood to those of skill in the art that the term FCP in the present disclosure is interchangeable with the term FICON because the disclosure of the invention set forth herein relates to the physical layer properties of these protocols. Fiber optic links have been defined for FCP protocol operating at several data rates as defined by ANSI. Currently, 1 Gbit/s and 2 Gbit/s links are most commonly used, although higher data rates such as 4 Gbits/s and above are beginning to emerge. Since FCP has become established as a critical enabler for computer networks, adopting higher bandwidth FCP links would be beneficial. FCP is defined as supporting 4 Gbit/s data rates over up to 10 km over single-mode fiber. The implementation of 4 Gbit/s and higher data rates over single-mode fiber with long wavelength (LX) sources (e.g., 1300 nm center wavelength) in a cost effective and efficient manner remains a challenge.
One way to support 4 Gbits/sec data rate is by using a distributed feedback (DFB) laser. A DFB laser can support a 4 Gbits/s data rate at 10 km over single-mode fiber, but tends to be expensive relative to Fabry-Perot lasers. The Fabry-Perot (FP) lasers are used reliably in lower data rate and shorter (e.g., 3-5 km) FCP links. To enable FP lasers to function at the 4 Gbit/s rate over 10 km additional complexity is required in the design to comply the FCP standard.
Short wavelength (SX) optical pulses, as well as LX pulses, present excessive dispersion as optical pulses propagate down the fuser with the implementation of 4 Gbit/s and higher data rates over multi-mode fiber with short wavelength (SX) light sources (e.g., 850 nm). Dispersion is a function of laser center wavelength and spectral width. SX links are typically specified in the range of 100-300 meters, compared with 10 km for an LX link. Even in fairly short optical links, dispersion is a limiting factor for BER performance.
Optical communication links require amplification (e.g., semiconductor optical amplifiers, semiconductor laser amplifiers, doped fiber amplifiers, etc.) to extend their distances for applications such as disaster recovery in a storage area network. Semiconductor optical amplifiers (SOAs) have proved useful in this regard. An SOA functions much like an in-line semiconductor laser diode that is optically pumped. In conventional applications which require extremely long distances, the most desirable conventional feature of the SOA is high gain. Conventional SOAs are designed with a broad spectral width to accommodate a wider range of input devices (and possible wavelength multiplexing in some cases). It amplifies incoming optical signals without requiring optical/electrical conversions.
The SOA is itself very similar in construction to a Fabry Perot semiconductor laser diode, using a mirrored optical cavity to affect gain in the direction of propagation for an optical signal. The mirrors are used to increase the effective path length through the gain medium, and hence increase the overall gain. The SOA may offer potential advantages over other optical amplification technologies such as doped fiber amplifiers. However, the invention disclosed herein may be practiced with any semiconductor optical amplifiers, i.e. amplifiers which can be biased with respect to their threshold setting and easily integrated with a laser package, as one known to those of skill in the art. The SOA can be monolithically integrated with other semiconductor devices on a common chip or substrate and mass produced at low cost. SOAs can easily amplify light at various wavelengths including 1300 nm and 850 nm. The SOA is a low cost solution to amplify the 1300 nm and 850 nm wavelength windows most commonly used in data communication systems such as FCP (other industry standards, including Ethernet, also use the same wavelength windows). SOAs are often used in gain clamping configurations. To optimize the achievable distance, SOAs may also be positioned near the middle of a long distance optical link.
U.S. Pat. No. 6,674,784, herein incorporated by reference, discloses a distributed feed back laser device. U.S. Pat. No. 6,584,126, herein incorporated by reference, discloses a tunable Fabry-Perot laser device and a vertical cavity surface emitting laser (VCSEL) device. U.S. Pat. No. 6,894,833, herein incorporated by reference, discloses a semiconductor optical amplifier used to amplify laser output. U.S. Pat. No. 6,839,481, herein incorporated by reference, discloses a multimode optical fiber system.